1. Field of the Invention
The present invention relates to a vibration transmitting unit that enables ultrasonic vibration to be transmitted, and an ultrasonic treatment instrument including the vibration transmitting unit.
2. Description of the Related Art
European Patent No. 2074955 specification discloses an ultrasonic treatment instrument including a vibration transmitting unit which is designed so as to vibrate at a standard resonance frequency by an ultrasonic vibration transmitted from a proximal side to a distal side. This vibration transmitting unit is provided with a plurality of cross-sectional reduction portions at which a cross-sectional area perpendicular to a longitudinal axis decreases towards the distal side. In a state where the vibration transmitting unit vibrates at the standard resonance frequency, all of the vibration anti-nodes are positioned away from each of the cross-sectional reduction portions in a direction parallel to the longitudinal axis. Therefore, stress caused by vibration acts on each of the plurality of cross-sectional reduction portions, thereby increasing the amplitude of the vibration. Furthermore, in the vibration transmitting unit, a cross-sectional increasing portion, at which a cross-sectional area perpendicular to the longitudinal axis increases towards the distal side, is provided between two cross-sectional reduction portions in a direction parallel to the longitudinal axis in a state where the vibration transmitting unit vibrates at the standard resonance frequency, one of the vibration anti-nodes is positioned at the cross-sectional increasing portion. Since a vibration anti-node in which stress caused by vibration becomes zero is positioned, the amplitude of the vibration does not decrease even at the cross-sectional increasing portion at which the cross-sectional area increases.